Current-limiting control for electric discharge devices



Jan. 30, 1945.

AMPBELL EIAL 2,368,410

CURRENT-LIMITING CONTROL FOR ELECTRIC DISCHARGE DEVICES Filed Jan. 16, 1942 lnven lrcjfs: John HCampbeLL ohn O.AiChT,

Patented Jan. 30, 1945 UNITED S TES PATENT OFFICE- cunann'r-mnrmo cou'rnor. ron ELEC- rnrc nrsormaca nov ces John H. Campbelland John 0. Aicher, Cleve- I land Heights, Ohio, assignors to General Electric Company, a corporation of New York Application January is, 1942, seria No. 427,034

' 9 Claims. (of. 176-122) This invention relates to electric discharge devices, and especially to current-limiting control for such devices; The .invention is very useful for fluorescent tubes or lamps of the usual positive column discharge type, and is hereinafter explained with particular reference to lamps of this character.

. As a general'rule, discharge devices or lamps require special provisions for limiting the dis-' charge current as against its natural tendency to increase automatically without any corresponding increase in the supply voltage,.as a result of which the lamp would run away and destroy itself. Such current-limiting means may assume various forms, such as ballast resistors or inductances, for example. Inductances or chokes are widely used, since they also serve to provide a temporary high voltage for starting in cases where the normal supplyvoltage is insufllcient for that purpose. Howeverythere are other ways of doing this; and in cases where the electrode gap of the discharge device is not too long and the other conditions in the device at starting are favorable, startingmay be effected on the normal operating voltage. This is true, for example,

as regards standard fluorescent lamps of 18 inch tube length, 1 /2 inch diameter, 14 or 15 watt rating, intended foroperation on supply circuits ,of 110-125 volts. Two such lamps can readily start and operate in series on a supply circuit of this voltage, as shown, for example, in United- States Patent 2,266,619, December 16,1941, John H. Campbell.

.The' necessity, forspecial current-limiting equipment such as chokes or resistors complicates fluorescent lamp installations and increases their cost. It also introduces a factor of uncertainty electrode mountsuch as shown in Fig. 1, on a larger scale; and Figs. 3 and 4 are similar views of modified forms of electrode mount.

Fig. '1 showsa fluorescent tube lamp L of the positive column electric discharge type with a tubular envelope 10 having spaced-apart thermioniccathodes H, H in its ends, which may be connected across a power supply circuit P meluding themanual make-and-break switch l3,

but without any current-limiting means therein.

into their operation, owing to the possibility that be used with unsuitable accessories. The resulting failure or unsatisfactory performance of the tion, including suitable operating and starting circuits diagrammaticallyrepresented; Fig. 2 is ,a fragmentary tilted or perspective view of an (through ignorance (fr-carelessness) lamps may The envelope I may contain a low-pressure atmosphere of, starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and also'a vaporizable and ionizable working substance such as mercury. A supply of mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop ll inside the envelope l0, and an internal coating of fluorescent material or phcmphor l5 on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown'connected across the circuit P through the filamentary cathodes, II, II, with a starting switch S included therein, which may be of thermal type or of any' other, suitable type. The lamp L is equipped with ordinary bipost bases i8 whence current leads [9, l9 extend into the interior of the envelope III, which is shown with separate glass end portions of stem and flare type.

As shown in Figs. 1 and 2, the cathodes ll H- are Just alike, and are of coiled or coiled-coil:

wire 22. One end of each wire 22 extends latera ally andat right angles to the coil 20, and has its lower extremity fused into the upper endoi the glass lamp mount stem 25. e other end portion 26 of each wire 22 is bent to extend parallel with the coil 20 to serve astan auxiliary anode during the positive half-cycles of operation.

The current-l'ead-wires l9, IQ of each lamp mount extend inward through the hollow stem 25' into the interior of the discharge envelope It, being sealed through the closed inner end of the stem as usual. The inner ends of these leads l2, l2 are preferably bent outward from one an other and then upward again, as shown at 29, 22. Between each lead-end 29 and the corresponding outer end of the cathode coil-20 a bal I 86- last resistance 2! is interposed and connected..

'P, and through the lamp as by welded joints 3|, 3|, being here shown as a coil or coiled coil more or less similar to the coil discharge between the cathodes 20, and preferably of tungsten, but unemissive or substantially so. In effect, therefore, the current leads 29, 29 are interconnected by three resistance members comprising an emissive ther mionic coil 20 with unemissive ballasting end coils 30, 30. The coil 20 maybe activated with a coating of refractory oxides, asof barium and strontium, as indicated by strippling, while the flanking ballast coils 30, 30 are unactivated and are preferably made of larger gauge wire than the coil 28, so as to insure that they shall be substantially unemissive under all conditions of operation.-

Theconstruction shown in Fig. 3 differs from that in Fig. 2 in having the lower ends of the cathode-coil support and connector wires 22, 22 insulatively connected to the upper ends of the lead wire i912, we (instead of to the upper end of the stem 25), as by means of glass beads 35, 35 into which the wire'ends are fused. Each ballast coil 30a extends up and down parallel with adjacent wires 22, [9a and has its ends bent at right angles to the coil and connected to said wires by welded joints 3m, Ma.

The construction shown in Fig. 4 differs from that in Fig. 3 in having an externally activated unipotential metal cathode tube 0 mounted around the tungsten wire coil 20b, which latter merely serves as a separate cathode resistance heater, without being itself effectively emissive. As shown, the ends of the tube 40 are closed by apertured end walls I, ll whose openings have insulative bushings 42, through which extend the coil connectors 22b, 22b. The cathode tube 40 is electrically connected to the mid-point of .the coil 20b, as diagrammatically indicated at M, so that its possible'circuit connections through the current leads I92), 191; are of equal resistance.

To avoid difliculties in lamp exhaust or in cathode activation, the connection 44 may in practice be made as shown in United States Patent 1,903,496, April 11, 1933, Beck, Fig. 2.

In Figs, 3 and 4, various parts andfeatures are marked with the same reference numerals as their homologues in Fig. 2, in order to dispense with repetitive description, distinctive letters being added where such distinction appears needful.

The discharge device L being connected in the circuits P and H as shown. in Fig. 1, a cold start of the lamp L may be initiated-by-closingthe switch l3, which causes current to flow-through both circuits-the starting switch S being mitially closed or quickly closing in response to energization of the circuit H,'if it is of glowswitch type. Current then flows through the circuits P, H and through each of the cathodes H,

Ii and both its associated ballast resistances 30, 30, preheating the .cathodecoils to proper emissive temperature. During this preheating and starting period, therefore, all four of the ballast resistances 30 are in circuit and are efiective to limit the current flow. When the switch S opens, substantially or nearly the full voltage of the supply line P is felt between the cathodes ll, and suflices to initiate a discharge between them. Thereafter the discharge current flows through the circuit P, the cathodes II', II, the two ballast resistances 30,- through which the cathodes are connected to the circuit two ballast resistances 30,30. are now out of circuit and ineflecldve; but the resistance to the the connections of the cathodes H, H to the supply line P (Fig. l) of suitable values, it is possible to 'omit the other two resistances 30, 30. This advantage, however, must be offset against the limitation of having either to polarize the device -L mechanically so as to positively prevent improper connection into the circuits P, H, or else to accept the destruction of lamps dueto unintelligent disregard of markings placed on them to indicate the proper mode of connection.

Moreover, the two resistances 3d, 30 must be of adequate values to take the place of the four shown in Fig. 1 during starting, while not of excessive values for subsequent normal operation of the device L.

The cathode and ballast arrangementsshown in Figs. 2, 3, and 4 all function substantially alike in the lam L. But the type of cathode shown in Fig. 4 affords the advantage of obviating radio interference due to proximity of the lamps to a receiving set, owing to the fact that the arc does not concentrate at one point on ,such a cathode as it does on the filamentary cathode now commonly used in fluorescent lamps, and hence does not produce the usual cathode sputtering which gives rise to interfering radio frequencies emanating from ordinary fluorescent lamps. In other words, lamps with the unipotential cathode give substantial freedom from both bulb radiation noise and line noise due to line feedback and line radiation.

For the convenience of those desiring to practice the invention, essential illustrative particulars of cathode mounts such as shown in Figs. 2 and 3 are here given:

The cathode 20 in Figs. sist. of a coiled coil of tungsten wire of 2.5 mil diameter, first wound 215 turns per inch on a 6 mil molybdenum mandrel to a. coil length of 44.9

and then wound turns per inch on a 22.6

mil molybdenum mandrel to a coil length of 1.6

time L. The other turns per inch on a 24 For each ballast coil mm. The total exposed length of actual wire'in the cathode coil 20 between the clamps 23, 23

.may amount to,252 mm, having a cold resistance of 4.4 ohms. The cathode coil 28 may be activated' with the usual oxide coating mixture of barium, strontium, and calcium oxides. Each of the ballasts 30 or 360. in Figs. 2 and 3 may consist of a coiled coil of tungsten wire of 2.75 mil diameter, first wound turns per inch on a 7 mil molybdenum mandrel, and then wound, 42 mil molybdenum mandrel. 38, 30:; may be used is turnsof the larger coil. with an exposed wire length of 354 mm. between the end-welds 3i, 3! or 3m, am, giving a cold resistance of 4.? ohms for each ballast. Of course both molybdenum mandrels for each coil 20 and :ill or 39:: are

removed after winding, in the usual way.

What we claim as new and desire to secure by mounts comprising a pair of current conductors 7 extending through a wall of said envelope and at 2 and 3 may con least two coiled filamentary resistance members in said envelope connected in series between said current conductors, one of said resistance members constituting a part of, one of the electrodes of the device, the said electrode also comprising electron-emissive material, another of said resistance members being substantially unemissive and serving as a ballast member, the unemissive resistance members in said pair of mounts being designed to serve as substantially the entire ballast during operation of the device, and the electrodes in said pair of mounts being spaced for a discharge therebetween.

2. A gaseous electric discharge device comprising a sealed envelope containing an ionizable medium and spaced mounts carrying electrodes and ballast resistances, each of said mounts comprising a pair of current conductors extending through a wall of said envelope and three coiled filamentary resistance members in said envelope connected in series between said current conductors, the second resistance member constituting a part of one of the electrodes of the device, the said electrode also comprising electron-emissive material, the first and third resistance members being substantially unemissive and serving as ballast members, the electrodes in said mounts being spaced for a discharge therebetween.

3. The combination set forth in claim 2 wherein the electrode in at least one of said mounts includes a metal shell surrounding said second resistance member and coated with electronemissive material and electrically connected to the midpoint of said second resistance member.

4. The combination set forth in claim 2 wherein the first and third ballast resistance members are made of heavier gauge wire than the second resistance member. a a

5. In a gaseous electric discharge device comprising a sealed envelope containing a pair of spaced electrodes between which the discharge occurs; one of said electrodes being incorporated in an electrode mount comprising a support member, a pair of lead-in conductors extending through said support member, and three coiled filamentary resistance members supported from said support member and connected in series between said lead-in conductors the second resistance member constituting a art of an activated lead-in conductors and said pair of unemissive resistance members serve as ballast members.

7. In a gaseous electric discharge device comprising a sealed envelope containing a pair of spaced electrodes between which the discharge occurs; one of said electrodes being incorporated I in an electrode. mount comprising a support member, a pair of lead-in conductors extending through said support member, a support conductor attached to but insulated from the end of each of said lead-in conductors to form a mechanical continuation thereof, a coiled filamenare all electrically connected in series between said lead-in conductors and said pair of unemissive resistance members serve as ba1last.members.

8. In a gaseous electric discharge device com prising a sealed envelope containing a pair of spaced electrodes between which the discharge occurs; one of said electrodes being incorporated in an electrode mount comprising a glass stem, 9. pair of support conductors extending from said stem and each having one end secured to said stem, a resistance member bridging said support conductors and supported thereby, said resistance" member constituting a part of an activated electron-emitting electrode, a pair of lead-in conducelectron-emitting electrode, the first and third resistance members being substantially unemissive and' serving as ballast members and being located betweenthe said support member and the said second resistance member.

6. In a gaseous electric discharge device comprising a sealed envelope containing a pair of spaced electrodes between which the discharge occurs; one of said electrodes being incorporated in an electrode mount comprising a support member,a pair of lead-in conductors extending through said support member, a support conductor attached to but insulated from the end of each of said lead-in conductors to form a mechanical continuation thereof, a coiled filamentary resistance member bridging and supported by said support conductors and constituting a part of ductor so that the said resistance members, are r 76 all electrically connected in series between said tors extending through said stem, and a'pair of substantially unemissive resistance members each mounted on and havingone end electrically connected to one of said lead-in conductors and the other end electrically connected to one of said support conductors so that the said resistancemembers are all electricallyconnected in series between said lead-in conductors and said pair of unemissive resistance members serve as ballast members.

9. In a gaseous electric discharge device comprising a sealed envelope containing a pair of spaced electrodes between which the discharge occurs; one of said electrodes being incorporated in an electrode mount comprising-an insulative support member, a pair of spaced lead-in wires extending inwardly through said support member, a, pair of conductors extending inwardly from the inner ends of said lead-in wires and secured thereto but insulated therefrom by glass beads fused to the adjacent ends of said wires and conductors, an activated electron-emitting electrode comprising a'coiled filamentary resistance member extending laterally between and connected to the inner ends of said conductors, and a pair of unemissive coiled filamentary resistance members located one on each side of the mount and between thefirst-mentioned resistance member and the support member, each of said pair of resistance members being mounted on and having its ends connected to the adjacent lead-in wire and conductor to complete a circuit around the associated glass bead thereby connecting all three resistance members in series, the said pair of resistance members serving as ballast members. JOHN H. CAMPBELL.

JOHN C. AICHER. 

